In recent years, a circuit board forming an electronic circuit by being mounted with electronic components has been miniaturized, and densification of circuit boards has been progressed. Among electronic components to be mounted on a circuit board, densification of a large scaled integrated circuit (LSI) has been progressed. With such a progress of densification, a number of external connection terminals of the LSI has been increased. On the other hand, the LSI is required to be miniaturized and densified. Thus, a ball grid array (BGA) type LSI, which is capable of being miniaturized while having a large number of pins, is used in many cases.
The BGA type LSI generally includes many solder-ball terminals as external connection terminals arranged in matrix on a mounting surface. Such a BGA type LSI is mounted to a circuit board by joining solder ball terminals to connection pads of the circuit board.
After mounting the LSI to the circuit board, an inspection is made as to whether all of the solder-ball terminals are joined to the respective connection pads of the circuit board. Each of the solder-ball terminals is once melted and solidified during a mounting process, thereby, forming a solder-joining part. Each electrode of the LSI is joined to the corresponding connection pad of the circuit board via the solder-joining part. Thus, by visually checking a state of the solder-joining part after mounting, a determination can be made as to whether each electrode of the LSI is appropriately connected to the corresponding connection pad of the circuit board via the solder-joining part.
However, because many solder-ball terminals are provided on the mounting surface of the BGA type LSI as mentioned above, it may be difficult to visually check many solder-joining parts existing in a narrow space between the circuit board and the LSI after the BGA type LIS is mounted to the circuit board. Thus, there is suggested an optical inspection method of inspecting a connecting state of solder joining parts by using an intensity of light (an amount of light) being irradiated to the solder-joining parts after mounting and passed through a space between the solder-joining parts (for example, refer to Patent Documents 1 to 3).
The following patent documents disclose a background art.
Patent Document 1: Japanese Laid-Open Patent Application No. 2001-144147
Patent Document 2: Japanese Laid-Open Patent Application No. 2006-41167
Patent Document 3: Japanese Laid-Open Patent Application No. 2000-346622
In a case where an inspection is made by detecting an intensity of transmitted light, which is irradiated onto one side of a space, in which many solder-joining parts are densely arranged, and transmitted to an opposite side of the space, if the density of the solder-joining parts is high and intervals therebetween become small, it may be difficult to detect a change in the transmitted light because an intensity of the transmitted light becomes low. Additionally, if the light is irradiated in a direction of alignment of the solder-joining parts, some of the solder-joining parts located at positions shaded by one of the solder-joining parts do not affect the transmitted light, and, thus, an inspection of the solder-joining parts cannot be done.
As mentioned above, in the case where an inspection is made on the solder-joining parts after an electronic component, such as a BGA type LSI having many solder-ball terminals arranged close to each other, is mounted to a circuit board, it may be difficult to make a reliable inspection if the above-mentioned inspection method using an intensity of a transmitted light is used.
Thus, it is desirous to materialize an electronic component inspection method and apparatus, which can make a reliable inspection on joint parts of an electronic component.